The present invention relates to an inspection apparatus for detecting whether collected sheet materials are normal or damaged and true or false and for re-accumulating disposable sheet materials and reusable sheet materials and to also a sheet material conveying device suited to this sheet material inspection apparatus.
To start with, a conventional sheet material inspection apparatus will be explained. The sheet material inspection apparatus is an apparatus which consecutively takes out collected sheet materials accumulated and fed in at a minute pitch by a take-out unit and thereafter checks whether the sheet materials are normal or damaged and true or false while conveying them on a belt at a high speed. The sheet material inspection apparatus then determines whether the individual sheet materials are to be disposed of or are reusable, thereafter distributes the sheet materials to branched conveying paths and re-accumulates the disposable sheet materials and the reusable sheet materials, separately.
The sheet materials accumulated as the disposable sheet materials by this apparatus are thereafter shredder-processed. A processing speed of the sheet materials in this inspection apparatus is on the order of 20-30 sheet materials/see, and a conveying velocity is always kept constant at 8 m/s.
FIG. 1 illustrates a construction of a sheet material conveying device employed in the conventional sheet material inspection apparatus. The transfer of the sheet materials involves independent driving sources and is conducted in such a way that the sheet material is grasped from at two portions in the crosswise direction by flat belts 61, 62 whose conveying surfaces are closely fitted to each other. These belts are driven by motors connected to drive rollers. Driving the belts at a high speed normally entails using motors each having a capacity on the order of several hundreds Watt.
As illustrated in FIG. 1, the rollers are disposed alternately on both sides of the conveying path to ensure the close fit between the belts. In the case of such a construction, the above and below belts have a trace of speed-difference, and, hence, a frictional force needs to be applied on both of the belts. For this purpose, the resistance of the conveying system is large, and a large force is required for driving the belts. Further, the belts run with a trace of oscillations in the crosswise direction, but, because of the surfaces being in contact with each other, the belts experience influences of the oscillations on each other. There exists a possibility in which this may cause the belts to come off the rollers. Moreover, the belts always press the upper and lower surfaces of the sheet material, and, consequently, there arises a problem in which the sheet material surface is concealed; and locations for detection are limited.
FIG. 2 depicts a conveying mechanism adopted in the case of conveying sheet materials at a low velocity. The sheet material is grasped between drive rollers 71 and rollers 72, and an up-and-down guide 73 is disposed between the rollers. Down-sizing and a reduction in weight in terms of the mechanism are attainable with this system. However, a leading edge of the sheet material is completely free between the guides and therefore collides with the rollers, easily resulting in damage. A defect is that this system is not suitable for conveying the sheet materials at a high velocity. Furthermore, the following problem also arises. A dispersion in the driving force between the respective rollers is produced by extrinsic factors such as abrasions, contaminations, and the like, on the roller surfaces. This dispersion in the driving force in turn causes a slippage, resulting in a difference in the conveying velocity of the sheet material between the respective rollers. As a result, a jam can easily occur.
The take-out unit for feeding out the sheet materials to the conveying path is constructed of a holed rotor for performing intermittent rotations and a static chamber connected to a vacuum pump. Every time the rotor stops, the take-out unit absorbs the sheet materials one by one from a stack of sheet materials accumulated and pulls it off the stack of sheet materials. The take-out unit thereafter puts the sheet material into the conveying system at a predetermined sheet material pitch (interval between the leading or trailing edges of the sheet materials fed adjacent to each other). A slight pitch error produced on the occasion of this take-out operation, means that the sheet materials having a minute pitch error are consecutively fed in the conveying system.
FIG. 3 schematically illustrates a structure of a sheet material accumulating unit in the prior art sheet material inspection apparatus. This sheet material accumulating unit is constructed mainly of an accumulation impeller 74. The accumulation impeller 74 is a rotary body having spiral blades at equal intervals with spiral grooves therebetween about the center thereof. The impeller 74 is belt-driven by a stepping motor 78. The sheet material fed in is stopped upon an insertion into the groove, thereafter scraped out of the groove and thus re-accumulated. The sheet materials are then transferred to the next processing.
Herein, for preventing a damage of the sheet material due to a jam and a collision with a blade, there is the need for assuring that only one sheet material is surely inserted into one line of groove. That is, the sheet materials fed in could have, as stated above, a pitch error. Accordingly, the sheet material accumulating unit is required to absorb this pitch error by use of some means and ensure the insertion of the sheet materials into the accumulation impeller 74. Then, according to the prior art, one point at a groove entrance of the accumulation impeller 74 is defined as an insertion point 75, and the control is effected to make the leading edge of the sheet material reach this insertion point 75.
Given next is an explanation of a control method of the accumulating unit in the conventional sheet material inspection apparatus.
A photoelectric sensor 76 is placed in a position across on the conveying path spaced away approximately 1 pitch from the accumulation impeller 74. When sheet material traverses this portion, an output of the sensor changes, thus detecting the leading edge of the sheet material. A rotary encoder 77 is connected to a motor 78 for driving the accumulation impeller 74, whereby a position of the in-rotation blade can be detected.
The sheet material leading edge reaches an optical path of the photoelectric sensor 76 and intercepts a beam of light, and, thus, the sensor output changes. Then, with this output serving as a trigger, a control unit (not shown) reads a value of the encoder 77 and predicts an insertion position of the relevant sheet material into the groove when the accumulation impeller 74 rotates at a standard rotating speed. At this time, if the sheet material deviates from the insertion point 75 of the groove, the control is carried out to correct this deviation. That is, if the leading edge of the sheet material is ahead of the insertion point 75 at the groove entrance, the control unit controls the stepping motor 78 to increase the rotating speed of the accumulation impeller 74. In the reverse case, the control unit controls the stepping motor 78 to decrease the rotating speed of the accumulation impeller 74. In any case, the rotating speed of the accumulation impeller 74 is determined to make the sheet material leading edge coincident with the insertion point. Thus an arithmetic operation is performed each time the sheet material reaches the position of the photoelectric sensor 76. The rotating speed of the accumulation impeller 74 is varied at all times to correct the pitch error between the respective sheet materials. For this reason, the stepping motor 78 always needs a control torque for an acceleration and a deceleration.
The sheet materials taken out are consecutively fed to the accumulation impeller 74. If the sheet material pitch does not undergo an influence by a disturbance or the like during the feed, however, it follows that the sheet material pitch just after being taken out continue to be kept. On the other hand, since a positional relationship between the blades adjacent to each other is fixed, the grooves of the accumulation impeller 74 can not be properly varied corresponding to the sheet material pitch. Accordingly, if the insertion position is shifted with a change in the rotating speed of the accumulation impeller 74 for an i-th sheet material, this shift directly turns out to be a deviation quantity of the (i+1)-th sheet material with respect to the accumulation impeller 74. That is, depending on the way how the sheet material pitch is scattered, if only the insertion position of the just-before sheet material is considered, the deviation quantity with respect to the sheet material subsequent thereto becomes excessive, As a result, a control quantity of the accumulation impeller 74, i.e., a control torque of the motor, becomes excessive, and hence there is a possibility of being incapable of control due to the fact that the motor is out of step. Particularly when speeding up the apparatus, this problem turns out a large obstacle.
In the prior art sheet material inspection apparatus, the insertion position is determined by only the sensor disposed immediately in front of the accumulating unit. Therefore, if the processing speed of the sheet materials is increased, it follows that the control torque needed for the stepping motor for rotating the accumulation impeller increases. This probably results in the incapability of control due to the stepping motor being out of step. Accordingly, the processing speed is conditioned by the control torque of the stepping motor, which hinders the speed-up thereof. For this reason, a high-speed and high-torque motor is needed. However, an unreasonable increment in the motor capacity brings about increases in size, in weight and in cost of the apparatus.
Furthermore, in the sheet material inspection apparatus using the conventional belts, it may happen that the belts come off A prevention of this requires a long time for strict adjustments of a belt tension, a roller inclination, and the like, and the productivity is not therefore favorable. Also, when conveying the sheet materials at high velocity, the motor increases in size, and the structure for attaining the down-sizing and the reduction in weight is hard to realize. The roller conveying system also easily damages the sheet materials and therefore unsuitable for high-speed driving.